In the manufacture of semiconductor devices, patterns such as integrated circuit interconnect patterns are formed by use of lithography. In the lithography process, light passing through a reticle (i.e., mask) that embodies a desired pattern is shone on a photosensitive resist film disposed on a semiconductor wafer, thereby printing the desired pattern in the resist film. A development process is then performed to remove needless portions of the resist film to form a desired resist pattern. When this is done, fine portions of the pattern may not be reproduced with sufficient accuracy. A corner of the pattern may be rounded and retreat. A notch portion may be rounded and expand. A fine line may become thinner and broken.
In a method referred to as hybrid exposure, both light exposure by use of a reticle and electron beam exposure are used to reproduce fine portions of a target pattern with sufficient accuracy. In general, fine line patterns with a pattern width narrower than a certain threshold among the given exposure patterns are assigned as electron-beam exposure patterns. Among the given exposure patterns, also, the perimeters of patterns with a pattern width wider than the threshold are extracted and assigned as electron-beam exposure patterns. Further, the core portions of these patterns with a pattern width wider than the threshold are extracted and assigned as reticle exposure patterns. The threshold may be set equal to 100 nm, for example. A reticle is formed based on the generated reticle exposure patterns. Light passing through the reticle is then shone on a resist film, thereby printing rough patterns. An electron beam is then shone on the resist film according to the electron-beam exposure patterns, thereby printing fine pattern portions.
An electron-beam exposure method draws patterns line by line, so that the excessive use of electron-beam exposure slows down the throughput of wafer production. When all the fine line patterns and all the pattern perimeters are categorically subjected to electron-beam exposure, portions for which sufficient accuracy can be attained by reticle exposure, i.e., portions for which electron-beam exposure may not be necessary, are all processed by electron-beam exposure that is time consuming. The use of a simple pattern classification method that determines electron-beam exposure patterns and reticle exposure patterns in a straightforward manner may end up excessively using electron-beam exposure. This results in a lengthy exposure process.
Patent Document 1 discloses a technology in which thresholds for line width and intervals are set as rules, and opposing pattern edges of exposure patterns are extracted based on these thresholds. The extracted pattern edge portions are then assigned as electron-beam exposure patterns. Other portions are assigned as reticle exposure patterns. The use of simple rules to reduce the number of electron-beam exposure portions may overcome the problem of lengthy exposure time. However, such practice may assign portions suitable for electron-beam exposure as portions for reticle exposure, resulting in lowered accuracy.
[Patent Document 1] Japanese Laid-open Patent Publication No. 04-155812